Powertrain control modules (PCM) are now widely used in automotive vehicles to control operations of the vehicle engine and multi-gear ratio automatic transmission. A PCM includes a microprocessor and suitable associated memory chips, input-output devices and the like and is programmed by a vehicle manufacturer to control engine and transmission functions such as air and fuel intake, spark timing and transmission shift schedules. The PCM receives data concerning engine and transmission operation from many electrical and electromechanical sensors.
In an automobile, the transmission is the component that transfers torque from the engine to the wheels to move the vehicle. The transmission does this by providing several forward gear ratios and one reverse gear ratio which enable the engine to accelerate the vehicle quickly, obtain high speeds and reverse the vehicle. An automatic transmission also allows the vehicle to stop while the engine is running without a manual clutch pedal. A torque converter provides this function by acting as a fluid coupling between the crank shaft and flywheel of the engine and the torque input to the transmission. Thus, in some operating modes of the powertrain, there is slippage in the torque converter and a difference between the speed of the engine and the speed of the output shaft of the transmission which cannot be determined from knowledge of the gear ratios of the transmission. This difference, e.g., in revolutions per minute (rpm), is known as slip.
The PCM requires certain inputs in order to control shifting of the forward gear ratios of the transmission. Such inputs include, for example, vehicle speed, throttle position, engine speed, present gear ratio, and transmission output speed. These inputs are provided by suitable electrical and electromechanical sensors associated with the drive axle, throttle and crankshaft, respectively, and electrically connected to the PCM. The PCM then sends signals to shift solenoids to cause suitable transmission upshifts and downshifts, to a transmission fluid pressure control solenoid to adjust shift feel, and to the torque converter control solenoid to engage or release the torque converter clutch. All such sensors must be designed, manufactured and assembled into the powertrain and maintained during vehicle life. For PCM shift scheduling purposes, it is also desirable for the computer to have data concerning torque converter slip because it is a parameter that significantly affects shift timing.
Torque converter slip is the difference between the torque converter input and output speeds. Torque converter input speed is equivalent to engine speed because the converter cover is bolted to the engine fly wheel and turns at engine speed. Data concerning engine speed is important to many PCM engine control functions, and a crankshaft position sensor is used to provide such information. Torque converter output speed is not measured, but in some powertrain designs a transmission input speed sensor (TISS) is used. Transmission input speed is the same as torque converter output speed, and when a TISS is available, the PCM can calculate torque converter slip whenever that data is required for shift control. However, a TISS is another device that must be assembled into the transmission, adding to the complexity and cost of the powertrain.
As increased and less inexpensive computer capacity becomes available for powertrain control use, it would be preferable, where possible, to estimate parameters such as torque converter slip from other available data rather than provide another expensive and, perhaps, vulnerable electromechanical device in the powertrain. Accordingly, it is an object of this invention to provide a virtual sensor for determining torque converter slip.